5 Boiler operation Rajan Bhandari Senior Lecturer Objectives

5. Boiler operation Rajan Bhandari Senior Lecturer

Objectives l l l Start a boiler safely from cold condition. Protect a superheater during boiler start up. Manage routine work involved for a boiler operating onload. Assess combustion quality of a boiler. Deal with abnormal operating conditions of a boiler in a safe manner.

Overview l The lesson briefly covers the recommended general procedures for the operation of auxiliary boilers (with or without a superheater) onboard ships. It looks at normal safe operational procedures as well as emergency operating conditions. Monitoring of combustion efficiency is also covered in the text.

Starting up a boiler l l l Check that the boiler is closed -up (especially after repairs). Check (physically) that all appropriate valves are shut or open for safe starting of the boiler. Boiler water filled to slightly below normal level. Starting treatment chemicals may now be added to the boiler water. Check and clear the furnace of any flammable materials. Ensure that the boiler uptake passage is clear.

Starting up a boiler l l Pre-purging of furnace for a specified amount of time is necessary to clear the gas-side of flammable gases, to avoid a starting explosion! On a cold boiler, the firing-up must not be speeded up too much in order not to overstrain the boiler material unnecessarily by quick, uneven temperature raises. Keep the boiler vents open until a heavy steam jet is flowing out (until a boiler pressure of about 1 bar is reached). Before the boiler is put on load, blowthrough the gauge glasses, test the safety valves using easing gear and try out the safety cutouts.

Boiler with integral super heater Keep superheater vent open and maintain flow

Flame should fill the furnace without any impingement. l Colour of flame should be moderately bright orange. l Colour of smoke as observed from the funnel should be brownish hazy. l

Oxygen: 3 to 4% by volume (for fire tube boilers), 0. 5 to 1. 5% by volume (for water tube boilers with high efficiency burners) l Carbon Dioxide: 12 to 14 % by volume. Higher the reading, the better is the combustion efficiency. It must be remembered that the. C 02 reading changes with the fuel type / quality and the level of excess air supplied to the burners l

Gross oil contamination The most dangerous water contamination is heavy fuel oil entering the boiler l the boiler could be completely destroyed due to overheating of the furnace l

Gross oil contamination Boiler taken off load / Shutdown Subsequently overflow the oily water through top manhole opening l Boiling out or chemical cleaning: l l l l Alkaline soak / degreasing using Sodium hydroxide or Phosphate Wash out Acid clean to remove milll scale Wash out and neutralise Passivate with Hydrazine or Alkaline chemicals

Small oil contamination Reduce the boiler load l Surface blow l Maintain Alkalinity by adding Alkaline chemicals l Add Anti-foam compound (if available) l

Effect of oil contamination Dark oily film in gauge glass l Foaming / priming l Overheating of boiler heat transfer surfaces l Acid formation and lowering of PH value of boiler feed l

Effect of high water level Reduce firing rate. Check & confirm high water level l Operate blowdown system. l Throttle feed check valves. l If bad water hammer due to carry-over is experienced, close steam outlet valve to prevent damage to pipe lines and machinery. l l

Water level below gauge glass l l l Shut-off burner (if not cut-out automatically). Take the boiler out of load. Confirm boiler water level by blowing through gauge glass. Ensure no internal damage due to overheating. Open and inspect internals Do not bring-up the water level in haste until the boiler parts are cooled down. Lowest visible water level Lowest permissible water level 51 mm 25 mm Heating surface

Survey of boiler accidents Reason for boiler failure Fire-tube Water-tube Mechanical, Electrical failures & Maintenance 35% 19% Boiler water troubles 17% 36% Personnel 16% 13% Corrosion and erosion 11 % 9% Installation and design deficiencies 10% 8% Defective material 8% 3% Others reasons - miscellaneous 3% 12% Note: The above tabulation is based on a survey of 250 water-tube boilers and 400 fire -tube boilers.

Water tube leak- detection Water tube Tube plate Remove Castable from here

Boiler tube leak - Plugging

Water tube leak- apply castable

Summary l l l Start a boiler safely from cold condition. Protect a superheater during boiler start up. Manage routine work involved for a boiler operating onload. Assess combustion quality of a boiler. Deal with abnormal operating conditions of a boiler in a safe manner.